For many years now, the techniques of ultrafiltration have been used in the milk and cheese industries.
French Patent 2 052 121, for example, describes a method which leads, through milk-ultrafiltration, to a concentrate of proteins--liquid pre-cheese--which is destined to the preparation of cheese, by addition therein of appropriate substances (rennet, lactic yeast, salt . . . ). French Patent 2 461 461 also describes the preparation of cheese from a swollen ultrafitration retentate, said preparation further involving the use of rennet. And it is also possible to prepare certain types of cheese--known as processed cheese--by adding processing salts to the ultrafiltration retentate.
French Patent 2 587 174 describes another use of the milk concentrate obtained by ultrafiltration. Sugar is added to it, and by heating the mixture, a food product is obtained which is known under the name of "milk jam".
Another patent, namely U.S. Pat. No. 4,497,834, also describes a method for preparing a food product--of spreading paste type--from milk. This method is based on a milk-concentration step by evaporation in vacuo, and on the baking of the resulting milk concentrate. To prevent graininess in the final product which is due to crystallization of lactose, the concentration of said product into said lactose has to be reduced, in the course of the method. The delactosing operation is advantageously carried out on the milk by enzymatic hydrolysis (lactase), by ultrafiltration or molecular sieving or by dilution.